With increasing development of science and technology, a tablet computer has been introduced into the market. The tablet computer is a mobile computer and often integrated into a flat, tablet screen, and may be primarily operated by touching the tablet screen. In a tablet computer, the processor may be part of the tablet screen. The tablet computer usually provides a user interface with the processor through the tablet screen. Via the tablet screen, the use may input an instruction into the tablet computer to control operations of the tablet computer. Generally, when the user wants to input a character or a symbol into the tablet computer, an on-screen keyboard is enabled and shown on the tablet screen of the tablet computer. The on-screen keyboard is a virtual keyboard simulating the real keyboard device. By touching an icon of the on-screen keyboard, a corresponding character or symbol is inputted into the tablet computer.